The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-283692 filed on Sep. 18, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a collision detecting apparatus for a vehicle, which outputs a collision signal for initiating a passenger protector for a vehicle, such as an air bag, upon collision of the vehicle.
2. Description of Background Art
With respect to a collision detecting apparatus to which the present invention pertains, as described in Japanese Patent Laid-open No. Hei 4-176757, a type of collision detecting apparatus is known that includes an integrating means for cumulatively integrating the output from an acceleration sensor when the output exceeds a specific calculation start level due to a collision of the vehicle. The collision detecting apparatus outputs a collision signal when a cumulative integral value calculated by the integrating means exceeds a specific threshold value.
Many types of collision apparatus for a vehicle exist depending on the collision state. For example, a usual collision apparatus is available wherein a deceleration, that is, a negative acceleration of the vehicle is gradually increased on the negative side due to an impact absorbing effect caused by deformation or breakage of the vehicle or an object against which the vehicle is collided immediately after collision (hereinafter, referred to simply as xe2x80x9cusual collisionxe2x80x9d). In addition, a severe collision apparatus is available wherein a large deceleration, that is, a negative acceleration abruptly occurs for a very short time due to the fact that a small absorption of the impact occurs immediately after collision for some cases (hereinafter, referred to simply as xe2x80x9crigid collisionxe2x80x9d).
For example, in the case of a motorcycle representative of the vehicle, an acceleration sensor is often mounted on a leading end portion of a front fork as shown in FIG. 5 (see Japanese Patent Laid-open No. Hei 11-278342). When a front wheel of the motorcycle collides against a relatively low rigid wall as shown in FIG. 5, a small amount of the impact energy is absorbed in the vehicular body, to cause the xe2x80x9crigid collisionxe2x80x9d. On the other hand, when a portion, located at a relatively high position, of the motorcycle collides against a counter-vehicle and thereby both the vehicles are deformed or broken, an impact energy is absorbed by an impact absorbing effect due to the deformation or breakage of the vehicles, to cause the xe2x80x9cusual collision.xe2x80x9d
According to a related art vehicle, however, since the threshold value is set to a constant value corresponding to the xe2x80x9cusual collision,xe2x80x9d even if a large deceleration rapidly occurs immediately after collision in the case of the xe2x80x9crigid collision,xe2x80x9d any collision signal is not outputted unless a cumulative integral value of the output from the acceleration sensor reaches the threshold value, to cause an inconvenience that the collision decision and thereby the operation of a passenger protector is retarded.
In view of the foregoing, the present invention has been made. It is an object of the present invention to provide a collision detecting apparatus for a vehicle that is capable of solving the above-described problem of the related art apparatus by accurately performing a collision decision with a high responsiveness irrespective of the state and severeness of the collision.
To achieve the above object, according to the present invention, there is provided a collision detecting apparatus for a vehicle including an acceleration sensor for detecting an acceleration upon collision of the vehicle, integrating means for cumulatively integrating an output from the acceleration sensor when the output exceeds a specific calculation start level, and collision detecting means for outputting a collision signal when a cumulative integral value calculated by the integrating means exceeds a threshold value. The collision detecting apparatus includes differentiating means for differentiating the output from the acceleration sensor and correcting means for correcting the threshold value on the basis of a differential value calculated by the differentiating means.
With this configuration, in the case of a usual collision in which an impact absorbing effect due to deformation of the vehicular body or the like can be somewhat expected, a collision signal is outputted from the collision detecting means when the cumulative integral value calculated by the integrating means exceeds a threshold value. Meanwhile, in the case of a rigid collision in which a deceleration (negative acceleration) of the vehicular body rapidly occurs, as an absolute value of the output differential value from the acceleration sensor becomes larger, the threshold value can be corrected so as to make the detecting sensitivity of the collision detecting means higher, so that a collision signal can be quickly outputted from the collision detecting means on the basis of the corrected threshold value. Accordingly, for the rigid collision, a collision decision can be quickly performed. As a result, since the collision decision can be accurately performed with a high responsiveness irrespective of the state of collision (that is, even if a deceleration is rapidly raised), the starting time of a passenger protector can be optimally controlled on the basis of the collision decision at any time.
According to the present invention, the correcting means stores the usual threshold value and a correction threshold value set on the side to make a detecting sensitivity of the collision detecting means higher than that for the usual threshold value, and the correcting means performs the correction by selecting the correction threshold value in place of the usual threshold value when the differential value exceeds a specific value. With this configuration, it is possible to correct the threshold value without the need of any special calculation, and hence to simplify the control.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.